This invention relates generally to electric blankets, and in particular, to an electric blanket incorporating an improved structure for heating the electric blanket and preventing the overheating of the same.
In colder climates, electric blankets are often used to keep individuals warm. Typically, an electric blanket includes first and second sheets of cloth material having a heating structure captured therebetween. The heating structure includes a heating core wire connectable to an electrical power source through a controller. The controller allows a user to vary the magnitude of the electrical power provided to the heating core wire, and hence, to control the heat dissipated by the heating core wire and the temperature of the electric blanket.
The heating core wire is contained in an insulation sheath that is protected by a woven screen. In normal use, an electric blanket should be spread out over a large surface area, such as a bed, in order for the whole surface to dissipate the heat generated by the heating core wire. It can be appreciated that the maximum temperature reached by the heating core wire must be below the melting point of the insulation. However, the risk of an electric blanket overheating may be significant in those situations when the heating core wire is electrically coupled to the electrical power source and the electric blanket is folded onto itself so as to prevent the heat generated by the heating core wire to escape. In such a situation, a first layer of the folded electric blanket may heat an adjacent layer (and vice versa) to such point as to cause the electric blanket to reach a temperature that is capable of starting a fire. It is noted, however, that the insulation about the heating core wire must melt before the cloth layers of the electric blanket begin to char and a fire starts.
In order to prevent the possibility of a fire starting due to the overheating of the electric blanket, most electric blankets incorporate a protective fuse circuit. The protective fuse circuit is usually connected to the woven screen. If the heater core wire overheats, the insulation softens and melts such that the heater core wire engages the woven screen causing a short circuit. The protective fuse circuit disconnects the heating coil wire from the electrical power source in response to the short circuit.
By way of example, it is contemplated that the protective fuse circuit include series resistor-diode combinations connected to corresponding ends of the woven screen. The resistors of the resistor-diode combinations are positioned adjacent a thermal fuse. In response to a short circuit between the heating core wire and the woven screen anywhere along the length of the heating core wire, current will flow through the resistor-diode combinations so as to heat the resistors. The thermal fuse is actuated by the dissipation of heat in the resistors so as to disconnect the heating coil wire from the electrical power source. It is noted that the conductive directions of the diodes of the resistor-diode combinations are opposed in order to prevent current flow through the protective fuse circuit unless there is a short circuit between the heating core wire and the woven screen. While functional for their intended purpose, these prior heating structures used in the electric blankets are relatively expensive. As such, it would be highly desirable to provide an electric blanket that utilizes less expensive components than prior electric blankets.
For electric blankets to be used on double beds, an additional design criteria must be considered. More specifically, multiple users of a single electric blanket may desire the electric blanket to be set to different temperatures. As such, electric blankets are often provided with independent heater structures and controllers for each side of the electric blanket. It can be appreciated that this type of arrangement requires a separate power outlet for each side of the electric blanket and/or additional pairs of wires directed to the heating structures for each side of the electric blanket. Therefore, it would be highly desirable to provide an electric blanket that uses a minimum number of wires and that has a single power outlet, but still allows for the independent control of the temperatures for each side of the electric blanket.
Therefore, it is a primary object and feature of the present invention to provide an electric blanket that utilizes a minimum number of wires and a less expensive components than prior electric blankets.
It is a further object and feature of the present invention to provide an electric blanket that allows for the independent control of the temperatures for each side of the electric blanket and that utilizes a single power outlet.
It is a still further object and feature of the present invention to provide an electric blanket that is simple and inexpensive to manufacture.
In accordance with the present invention, an electric blanket is provided. The electric blanket includes a first core wire having first and second ends. A second core wire is positioned adjacent the first core wire. The second core wire engages the first core wire in response to a predetermined temperature. A cutout is operatively connected to the first end of the first core wire. The cutout is movable between a first connected state wherein the cutout electrically couples the first end of the first core wire to a variable power source and the second disconnected state wherein the cutout disconnects the first end of the first core from the variable power source. A monitoring circuit is operatively connected to the second core wire. The monitoring circuit moves the cutout between the connected state and the disconnected state in response to engagement of the second core wire and the first core wire.
The first and second core wires are wrapped in insulation. The insulation melts in response to exposure to a predetermined temperature. The second core wire has first and second ends. The monitoring circuit includes a first resistor and diode combination interconnecting the first end of the second core wire and a neutral point. The monitoring circuit further includes a second resistor and diode combination interconnecting the second end of the second core wire and the first end of the first core wire. The first and second resistor and diode combinations are interconnected in series. The diodes of the resistor and diode combinations have predetermined conductive directions and the conductive directions of the diodes of the resistor and diode combinations are opposed. It is contemplated to position the cutout in close proximity to the resistors of the first and second resistor and diode combinations.
The electric blanket may also include a third core wire positioned adjacent the second core wire. The third core wire has a first end operatively connected to the second end of the first core wire and a second end operatively connected to a neutral point. The monitoring circuit moves the cutout between the connected state and the disconnected state in response to engagement of the second core wire and the third core wire. The cutout may include a thermal fuse.
In accordance with a further aspect of the present invention, an electric blanket is provided. The electric blanket includes a first heater having a first heating wire, a second heating wire and a monitoring wire. The first heating wire has a first end and a second end. The second heating wire has a first end operatively connected to the second end of the first heating wire and a second end operatively connected to a first neutral point. The monitoring wire is positioned between the first and second heating wires. The monitoring wire is engageable with the first and second heating wires in response to a predetermined temperature. A cutout is operatively connected to the first end of the first heating wire. The cutout is movable between the first connected state wherein the cutout electrically couples the first end of the heating wire to a variable power source and a second connected state wherein the cutout disconnects the first end of the first heating wire from the variable power source. A monitoring circuit is operatively connected to the monitoring wire. The monitoring circuit moves the cutout between the connected state and the disconnected state in response to engagement of the monitoring wire with one of the heating wires.
The electric blanket may also include a second heater. The second heater has a first heating wire, a second heating wire and a monitoring wire. The first heating wire of the second heater has first and second ends. The second heating wire of the second heater has a first end operatively connected to the second end of the first heating wire of the second heater and a second end operatively connected to a second neutral point. The monitoring wire of the second heater is positioned between the first and second heating wires of the second heater. The monitoring wire of the second heater is engageable with the first and second heating wires of the second heater in response to a predetermined temperature.
The cutout of the electric blanket is operatively connected to the first end of the first heating wire of the second heater such that with the cutout in the first connected state, the cutout electrically couples the first end of the first heating wire of the second heater to the variable power source, and with the cutout in the second disconnected state, the cutout disconnects the first end of the first heating wire of the second heater from the variable power source.
The electric blanket may also include a second monitoring circuit operatively connected to the monitoring wire of the second heater. The second monitoring circuit moves the cutout between the connected state and the disconnected state in response to engagement of the monitoring wire of the second heater with one of the heating wires of the second heater.
The monitoring wire of the first heater has first and second ends. The first monitoring circuit includes a first resistor in diode combination interconnecting the first end of the monitoring wire of the first heater and a second neutral point. The resistor and the diode of the first resistor and diode combination are operatively connected at a node. A second resistor and diode combination interconnects the second end of the monitoring wire of the first heater and the first end of the first heating wire of the first heater. The monitoring wire of the second heater has first and second ends. The first resistor and diode combination interconnects the first end of the monitoring wire of the second heater and the second neutral point. The second resistor and diode combination interconnects the second end of the monitoring wire of the second heater and the first end of the first heating wire of the first heater. The first and second resistor and diode combinations are connected in series. The diodes of the resistor and diode combinations have predetermined conductive directions. The conductive directions of the diodes of the resistor and diode combinations are opposed. A fault current diode having a predetermined conductive direction may be interconnected to the first neutral point and the node. The conductive direction of the fault current diode and the conductive direction of the diode of the first resistor and diode combination are opposed.
In accordance with a further aspect of the present invention, an electric blanket is provided. The electric blanket is connected to a power source for providing voltage and current thereto. The electric blanket includes a first heater having a first end connectable to the power source and a second end connectable to a first neutral point. The first heater includes first and second heating elements connected in series. A first monitoring wire is disposed between the first and second heating elements. The first monitoring wire is engageable with a least one of the heating elements in response to a predetermined temperature. A monitoring circuit is operatively connected to the first monitoring wire and to the power source. The monitoring circuit disconnects the first heater from the power source in response to the first monitoring wire engaging at least one of the heating elements.
The electric blanket may also include a second heater having a first end connectable to the power source and a second end connectable to a second neutral point. The second heater includes first and second heating elements connected in series. A second monitoring wire is disposed between the first and second heating elements of the second heater. The second monitoring wire is engageable with at least one of the heating elements of the second heater in response to a predetermined temperature. A second monitoring circuit may be operatively connected to the second monitoring wire and to the power source. The second monitoring circuit disconnects the first heater from the power source in response to the second monitoring wire engaging at least one of the heating elements of the second heater.
It is contemplated to interconnect the first end of the first heater and the first end of the second heater at a heater node. The first end of the monitoring wire and the first end of the second monitoring wire may be operatively connected at a first monitoring wire node. The second end of the first monitoring wire and the second end of the second monitoring wire may be operatively connected at a second monitoring wire node. A first resistor and diode combination interconnects the first monitoring wire node and the second neutral point. The resistor and the diode of the first resistor and diode combination are operatively connected at a resistor-diode node. A second resistor and diode combination interconnects the second monitoring wire node and the heater node. The first and second resistor and diode combinations are connected in series. The diodes of the resistor and diode combinations have predetermined conductive directions. The conductive directions of the diodes of the resistor and diode combinations are opposed.
It is contemplated that the electric blanket include a fault current diode having a predetermined conductive direction. The fault current diode interconnects the first neutral point and the resistor-diode node. The conductive direction of the fault current diode and a conductive direction of the diode of the first resistor and diode combination are opposed.